At about 8:00 A.M. today (October 15, 2013), a very strong earthquake struck the Central Visayas region. The earthquake's epicenter was located near Cabigtian town in Bohol Island. The earthquake also affected parts of Mindanao and nearby islands, particularly Cebu. Bohol and Cebu took the brunt of the earthquake, both islands suffered extensive infrastructure damage and quite a number of casualties. Determining the extent of damage and the number of casualties in both provinces is still in progress up to this moment.
February 6 of last year, the same area was also struck by an earthquake of almost the same magnitude as the temblor today. Then, the island of Bohol was slighlty affected by the temblor and spared from any damage. This time the whole island of Bohol is much affected, and devastated at that. Bohol's booming tourist industry will surely suffer in the aftermath of the earthquake. Quite a number of its historical century-old Catholic churches collapsed or were partially destroyed. Even the province's main tourist attraction : the famous"Chocolate Hills" were not spared from landslides.
The strength of the Bohol earthquake was described by Phivolcs Director Renato Solidum as : “A magnitude seven earthquake has an energy equivalent to around 32 Hiroshima atomic bombs. This one had a magnitude of 7.2.”
Bohol Island has its own faultline : the East Bohol Fault (see picture below). Movements of faults and tectonic plates normally cause earthquakes.
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| USGS ShakeMap : Octber 15, 2013 Bohol Earthquake |
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| Active Earthquake Faultlines of Bohol, Cebu and Negros Islands |
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| Bohol Earthquake Epicenter |
 Types of Earthquake Faultline Movement |
Normal faults are dip-slip faults within the upper plate (the upper portion of the inclined fault) subducting. Reverse faults are dip-slip faults with the upper plate rising. When people stand facing a fault, the right-lateral strike-slip faults are those in which the far surface has lateral slip to the right, while left-lateral strike-slip faults are those in which the far surface has lateral slip to the left.
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According to the US Geological Survey, the Bohol earthquake was due to reverse faulting movement of a faultline. ( see illustration above ) :
"The October 15, 2013 M 7.1 earthquake near the city of Catigbian on Bohol Island, Philippines, occurred as the result of shallow reverse faulting on a moderately inclined fault dipping either to the northwest, or to the southeast. The depth of the event indicates it ruptured a fault within the crust of the Sunda plate, rather than on the deeper subduction zone plate boundary interface. At the latitude of this earthquake, the Philippine Sea plate moves towards the west-northwest with respect to the Sunda plate at a rate of approximately 10 cm/yr, subducting beneath the Philippine Islands several hundred kilometers to the east of the October 15 earthquake at the Philippine Trench."
"The Philippine Islands straddle a region of complex tectonics at the intersection of three major tectonic plates (the Philippine Sea, Sunda and Eurasia plates). As such, the islands are familiar with large and damaging earthquakes, and the region within 500 km of the October 15 earthquake has hosted 19 events of M6 or greater, a dozen of which have been shallow (0-70 km). One of these, a M 6.8 earthquake 70 km to the east of the October 15, 2013 event in 1990, caused several casualties."
Source : http://earthquake.usgs.gov/earthquakes/eventpage/usb000kdb4#summary
Source : http://earthquake.usgs.gov/earthquakes/eventpage/usb000kdb4#summary
My prayer goes to all the people affected by the earthquake. And I fervently wish and pray that God heals our land soon.
Reminder :
Our fellow Filipinos affected by the earthquake in Bohol and Cebu surely need help now and in the days to come. Let's help them in anyway we can. Please don't forget to send your donations. God Bless everyone!
Picture and Map Sources :
http://www.hp1039.jishin.go.jp/eqchreng/af1-2.htm
http://www.phivolcs.dost.gov.ph/images/active.faults/af_trench_with_capitals.pdf
http://earthquake.usgs.gov/earthquakes/eventpage/usb000kdb4#summary
Related Link :
http://theprojectreview.blogspot.com/2012/02/information-february-6-negros-and-cebu.html
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